Division of Endocrinology and Metabolism, Department of Medicine, Royal Victoria Hospital, McGill University Health Centre Research Institute, McGill University, Montreal, Quebec, Canada.
PLoS One. 2010 Dec 28;5(12):e15662. doi: 10.1371/journal.pone.0015662.
C. elegans first stage (L1) larvae hatched in the absence of food, arrest development and enter an L1 diapause, whereby they can survive starvation for several weeks. The physiological and metabolic requirements for survival during L1 diapause are poorly understood. However, yolk, a cholesterol binding/transport protein, has been suggested to serve as an energy source. Here, we demonstrate that C. elegans TBC-2, a RAB-5 GTPase Activating Protein (GAP) involved in early-to-late endosome transition, is important for yolk protein storage during embryogenesis and for L1 survival during starvation. We found during embryogenesis, that a yolk::green fluorescent protein fusion (YP170::GFP), disappeared much more quickly in tbc-2 mutant embryos as compared with wild-type control embryos. The premature disappearance of YP170::GFP in tbc-2 mutants is likely due to premature degradation in the lysosomes as we found that YP170::GFP showed increased colocalization with Lysotracker Red, a marker for acidic compartments. Furthermore, YP170::GFP disappearance in tbc-2 mutants required RAB-7, a regulator of endosome to lysosome trafficking. Although tbc-2 is not essential in fed animals, we discovered that tbc-2 mutant L1 larvae have strongly reduced survival when hatched in the absence of food. We show that tbc-2 mutant larvae are not defective in maintaining L1 diapause and that mutants defective in yolk uptake, rme-1 and rme-6, also had strongly reduced L1 survival when hatched in the absence of food. Our findings demonstrate that TBC-2 is required for yolk protein storage during embryonic development and provide strong correlative data indicating that yolk constitutes an important energy source for larval survival during L1 diapause.
秀丽隐杆线虫第一阶段（L1）幼虫在没有食物的情况下孵化，停止发育并进入 L1 休眠，从而可以在饥饿状态下存活数周。对于 L1 休眠期间的生存，其生理和代谢需求还了解甚少。然而，卵黄是一种胆固醇结合/转运蛋白，被认为是一种能量来源。在这里，我们证明秀丽隐杆线虫 TBC-2，一种参与早期到晚期内体转变的 RAB-5 GTP 酶激活蛋白（GAP），对于胚胎发生期间卵黄蛋白的储存以及饥饿期间 L1 的存活很重要。我们发现，在胚胎发生过程中，与野生型对照胚胎相比，卵黄::绿色荧光蛋白融合物（YP170::GFP）在 tbc-2 突变体胚胎中消失得更快。YP170::GFP 在 tbc-2 突变体中的过早消失很可能是由于溶酶体中的过早降解，因为我们发现 YP170::GFP 与 Lysotracker Red（酸性隔室的标志物）的共定位增加。此外，YP170::GFP 在 tbc-2 突变体中的消失需要 RAB-7，它是内体到溶酶体运输的调节剂。尽管 tbc-2 在喂养动物中不是必需的，但我们发现，当在没有食物的情况下孵化时，tbc-2 突变体 L1 幼虫的存活率大大降低。我们表明，tbc-2 突变体幼虫在维持 L1 休眠方面没有缺陷，并且在没有食物的情况下孵化时，卵黄摄取缺陷突变体 rme-1 和 rme-6 也具有强烈降低的 L1 存活率。我们的研究结果表明，TBC-2 是胚胎发育过程中卵黄蛋白储存所必需的，并提供了有力的相关数据，表明卵黄是 L1 休眠期间幼虫存活的重要能量来源。
